Silver salt diffusion process

ABSTRACT

SILVER SALT DIFFUSION TRANSFER METHOD IN WHICH THE RECEIVING MATERIAL PRIOR TO CONTACT WITH THE NEGATIVE MATERIAL IS MOISTENED WITH A LIQUOR AND SQUEEZED. A SECOND SQUEEZING TAKES PLACE WHILE THE RECEIVING MATERIAL AND THE NEGATIVE ARE IN CONTACT WITH EACH OTHER.

United States Patent O 3,711,281 SILVER SALT DIFFUSION PROCESS Walter Limberger, Hamburg-Poppenbuettel, Germany, assignor to Lumoprint Zindler KG, Hamburg, Germany No Drawing. Original application Nov. 22, 1966, Ser. No. 596,221. Divided and this application Dec. 9, 1969, Ser. No. 883,637 Claims priority, application Germany, Nov. 25, 1965, P 15 72 111.6 Int. Cl. G030 5/54 US. Cl. 96-29 R 4 Claims ABSTRACT OF THE DISCLOSURE Silver salt diffusion transfer method in which the receiving material prior to contact with the negative material is moistened with a liquid and squeezed. A second squeezing takes place while the receiving material and the negative are in contact with each other.

CROSS REFERENCE TO PRIOR APPLICATION This is a divisional application of Ser. No. 596,221; filed Nov. 22, 1966.

The invention relates to a silver salt diffusion transfer process using a negative material, on the silver halide emulsion layer of which an image is formed by exposure, and a receptor or receiving material, to which the image is transferred, wherein the exposed negative material is moistened with a liquid for effecting development and is subjected to compression in contact with the moistened receptor material of paper, film or textile materials.

In German specification No. 764,572, the so-called silver salt diffusion process is described and it is stated that various materials are used as the receptor image carrier, for example uncoated papers, textiles, wood, celluloid and other synthetic materials and the like. It may be mentioned that the expression material as used herein means any material of sheet form.

The afore-mentioned specification states that the transfer can be assisted by the presence of materials which favor diffusion. The diffusing or diffused silver halide can be developed imagewise without exposure, this development being assisted by added nuclei or reactants. The developed image is applied for instance to a baryta paper or a textile support which has been moistened in the same bath as the silver halide material.

In carrying out the process in practice as it has been developed for commercial use employing sheet-like copy materials, a separate positive or receptor layer has been provided, in which the reduction nuclei are contained. This layer is generally provided on a special support, so that the layer and the support form the receptor material.

It is also known to use the receptor layer independently of a support and apply it for instance as a cover layer or overcoating on the negative layer. Such a system is described in specification No. 1,171,740 and uses colloidal overcoatings and receptor layers. No reduction nuclei need be contained in this layer. According to specification No. 1,171,740, reduction nuclei are supplied to the colloidal receptor layer by means of the treating liquid. The reduction nuclei canbe provided according to the specification mentioned as sulphides, selenides, polysulphides, polyselenides, thiourea, mercaptans, tin haldies, heavy metals or their salts as well as fogged silver halides and sulphides of heavy metals such as antimony, bismuth, cadmium, cobalt, lead, nickel and silver. Heavy metals, for instance silver, gold, platinum, palladium and mercury, preferably in colloidal form, are considered the most effective. The noble metals are particularly preferred.

In the method according to specification No. 1,171,740, the image-receiving layer provided in the usual way is thus arranged as an overcoating on the negative and a sheet is provided for receiving the image developed in the overcoating. Since according to specification No. 764,572 a difficultly-soluble silver compound or colloidal silver, which is produced in the receptor layer, is to be considered non-diffusible, the colloidal overcoating or image receptor layer containing the developed image is during transfer thus also transferred to the receptor sheet paper or the like.

In other copying methods, it is already possible to transfer a usable image to a normal paper sheet without using a positive layer. This applies, however, to physical methods, such as the electrophotographic method for instance.

German specifications Nos. 764,572 and 1,717,740 are based on the use of reduction nuclei, as they have already been used in practice in the silver salt diffusion process known as the Copyrapid method.

If the reduction nuclei, according to specification No. 1,171,740, are provided in the treating liquid which not only serves to carry out development, but also for the formation of complex salts of the unexposed and undeveloped silver halide, the same limitations arise with regard to the stability of such solutions as are known to exist with developers used in the silver salt diffusion process. These limitations are due to the simultaneous presence of atmospheric oxidation products and used and unused developer substances, the increasing content of silver halide solvents caused by the increasing number of copies and silver halide complex compounds which diffuse into the solution and may be active as reduction nuclei.

DETAILED DESCRIPTION OF THE INVENTION The invention has as its task to provide a process which allows the economic formation of a positive image on an uncoated support by means of the silver salt diffusion process, wherein the liquids used have satisfactory stability and productiveness.

The expression uncoated support means a sheet, e.g. of paper, which contains no film-forming colloids, but for which only a moistening with an aqueous solution is to be provided.

A further object of the invention is to enable the use of simple and inexpensive materials.

A further object of the invention is to provide a process wherein, for carrying out the transfer process, one of the materials can be used uncoated, so that the problem of providing multiple coatings on a support are avoided. With the production of multiple coatings, the possibility arises, probably with long storage and/or through changing effects of atmospheric moisture and temperature, that damage can occur, especially if special binding agents are not provided.

In contrast to known methods, it is novel to moisten the receptor material with another liquid before associating it with the negative material, which other liquid contains reduction nuclei or substances forming reduction nuclei and a silver salt solvent in aqueous solution. Such procedure has the advantage of operating without a filmforming colloid receptor layer and normal diffusion negative material is usable. Further advantages reside in the composition of the liquids used due to their stability and to the possibility of making a larger number of copies. It has surprisingly been shown that, for example, using the so-called Copyrapid dry negative material, a trade name of Agfa Gevaert A.G., or the so-called Kodak dry paper which are commercially available, substantially better results can be obtained with the method according to the invention. Such use is therefore a further embodiment of the invention. Separate moistening of the receptor material and of the negative matenial with different liquids, thus saving a receptor layer in the actual sense per se, leads to satisfactory copies if the two materials 3 are brought together in the moist state and subjected to pressure.

The moistening does not extend to a so-called coating. Such an operation is known for example from German specification No. 1,168,927. This relates to a coating process on uncoated paper for carrying out a heat copy method, which provides that the original is subjected to infra-red radiation in surface-to-surface contact with the coated support. It is therefore necessary to dry the coating solution before bringing it together with the original, in order not to damage the original.

In this known method, no diffusion or transfer process is involved, but a definite coloration at a predetermined temperature corresponding to the selective heating caused by the radiant energy absorbed by the dark characters of the original.

In contrast and according to the invention, a receptor material is used which, after moistening, is subjected to wiping or squeezing at least on the moistened side and is brought into contact with the negative material. This wiping or squeezing apparently not only has the effect of removing the liquid, but liquid is also forced with a uniform distribution, at least into the moistened surface, whereby no liquid film remains on the surface and therefore the formation or precipitation of silver halide compleX salt dilfusing from the negative does not take place in the liquid film, but on the paper surface. Surface precipitation of the diffusing salt on to the surface likewise is favored by the fact that the reduction nuclei are present in the dissolved state in the receptor sheet. If instead of drect moistening and wiping or squeezing, factory preparation and drying of the receptor material would be provided for, a loss in quality of about 50% would occur as regards darkening of the silver image, since the nuclei would be uniformly distributed in the material and a silver salt precipitate picture of the diffusing complex salt would be formed which penetrates the depth of the paper thickness.

The invention therefore provides that the receptor material is subjected to two separate squeezing operations, the first of which takes place before bringing it into contact with the negative material and the other after bringing it into contact and while still in contact with the negative material.

The invention is based, on the one hand, on separate moistening of the two materials, a procedure which is by no means obvious and itself leads to significant advantages and, on the other hand, on the use of a material, namely the receptor material, which is subjected to a treatment which leads to a surprising result. This treatment is a combination of the application of the chemical liquid and a mechanical action, which in co-operation considerably improve the result.

Where reference is made to moistening, it is also possible to moisten merely one side of the sheet receptor material, namely that side on which the image is formed. Moistening can be carried out in any suitable way, such as by spraying, application by means of a moistening roller or the like. Advantageously, the receptor material is advanced in known manner through the liquid and is subjected to roller squeezing before contacting the negative material. Roller squeezing has the advantage that, apart from the above-described effect, excess liquid is removed. Double squeezing of the receptor material leads to drier copies than previously possible and the undesirable roller effect on the copies is safely avoided.

According to a particularly preferred embodiment, commercial Copyrapid dry negative paper or Kodak dry paper is used as the negative material and an activator provided for these materials is used as the developer liquid. In using normal silver salt diffusion negative papers, a developer commercially available for such papers is also used.

To improve the economics of the method, an important feature consists in using, as the treating liquid for the 4 receptor material, a solution with a concentration of about 0.02% hexachloroplatinic (IV) acid and/or gold (11]) chloride hydrochloric acid. It has been ascertained that, for the reasons mentioned above, by using such a liquid substantially more copies can be made than if the nuclei are contained in the developer liquid itself.

Where reference is made to reduction nuclei, there is the possibility, if required, of using a combination of such nuclei.

The present invention is characterized in that not only are the treatment baths simple, stable and relatively inexpensive, but they lead to a commercially utilizable method in which ordinary papers can be used, without additional coatings on the negative'materials having to be provided.

If additional coatings were provided, the advantages of being able to use a simple paper sheet as the receptor material would be substantially lost by the more complicated construction of the negative.

It has also been found that it is not possible, using the features described, to use ordinary preprepared papers which are produced by immersion with an aqueous solution of a composition necessary for treating the receptor material and subsequent drying. Such a procedure does not lead to the desired result. The invention therefore provides in its simplest form not only a new method in which the time for the occurrence of the chemical and physical phenomena is chosen at will, but it also depends on a predetermined timely sequence of operational steps in which the receptor material must be moistened with a certain liquid immediately before contacting the transfer material.

The terms used in the following examples for the liquid have the following meaning:

H O Dist. water.

Mirasol 0.5% soln. in H 0 (wetting agent). Na S o -soln Sodium thiosulphate 1% in H O. Ag NO -soln. 1% silver nitrate soln. in H O. Gold-soln. 1% gold (III) chloride hydrochloric acid, yellow, in H O, H(AuCl -4H O. Platinum-soln 1% hexachloroplatinic (VI) acid,

dry in H O.

61 1000 ml. H 0. 15 ml. Mirasol.

Example? 20 ml. Ag. NO -soln. 40 ml. Na S O -soln. 1000 ml. H O.

Example H 15 ml. Mirasol.

20 ml. gold-soln.

10 ml. Na S O -soln. 1000 ml. H O.

15 ml. Mirasol.

5 ml. gold-soln.

1 ml. Na S O -soln. 1000 ml. H 0.

15 ml. Mirasol.

10 ml. platinum-soln. 5 ml. Na s o soln. 5 ml. gold-soln.

1000 ml. H 0.

15 ml. Mirasol.

10 ml. platinum-soln. 5 ml. Na s O -soln. 10 ml. gold-soln.

Example III Example IV Example V What is claimed is:

1. In a silver salt diifusion transfer method, in which an image is formed by exposure on a silver halide emulsion layer of a negative material, and the exposed layer of the negative material is moistened with a first liquid for eifecting development of the image which is transferred to a receiving material by pressing together the layer of the negative material and the receiving material and wherein the receiving material is an uncoated sheet which, prior to contact with the layer of the negative material, is moistened with a second liquid containing in aqueous solution reduction nuclei or substances forming reduction nuclei and a silver salt solvent, the improvement which comprises that the receiving material, after moistening with said second liquid but before contact with said negative material, is squeezed, whereby an amount of said second liquid is forced into said receiving material.

2. The improvement of claim 1 wherein the receiving material is passed through said second liquid and the squeezing is effected by subjecting the moist receiving material to roller squeezing.

3. A process according to claim 1, wherein commercial Copyrapid dry paper or Kodak dry paper is used as the negative material and an activator for such paper is used as the first liquid.

4. A process according to claim 1, wherein a solution with a concentration of about 0.02% of a hexachloroplatinic (IV) acid and/or a gold (III) chloride hydrochloric acid is used as the second liquid.

References Cited UNITED STATES PATENTS 3,072,480 1/1963 Abbott et a1 9629 3,042,514 7/ 1962 Roth 9629 3,450,535 6/1969 Limberger et a1. 96-29 3,510,301 5/ 1970 Limberger 9629 1,405,198 1/1922 Frothingham et a1. 1171 11 R J. TRAVIS BROWN, Primary Examiner J. L. GOODROW, Assistant Examiner 

